1. Field of the Invention
The present invention relates to an oscillator for generating clock signals (for example, clocks for use in counting a memory write period).
2. Description of Related Art
In recent years, non-volatile semiconductor memories (for example, an EEPROM (electronically erasable and programmable read only memory)) have been widely used for various types of data storage (such as for automatically controlling filter characteristics, amplification and the like, performing localization and storing state information prior to turning off of power) in consumer devices, industrial devices and other devices
JP-A-2002-093162 (hereinafter called patent document 1) is an example of conventional technology related to the foregoing.
The write period for a semiconductor memory depends on the oscillating frequency of a clock signal generated by an oscillator. Thus, oscillators used in such an application are required to generate clock signals of stable oscillating frequency over a wide range of power supply voltages.
In the fields of mobile telephones and camera modules, semiconductor memories are required to be driven with a low voltage (a 1.7 volt drive). Oscillators used in such applications are not only required to be driven with a low voltage, but also required to maintain a proper oscillating frequency characteristic while being driven with a low voltage.
In oscillators incorporated in semiconductor memories and even oscillators in other applications, the important problem to be solved is to provide a stable oscillating frequency and a low voltage drive.